1. Field of Invention
This invention relates to a failure detection device for detecting failure of a rotation angle detection sensor, which sensor detects the angular position of a rotatable member.
2. Description of Related Art
Conventionally, in a vehicle where shift control is performed by an A/T (Automatic Transmission) or a CVT (Continuously Variable Transmission), when a range is selected by operation of a shift lever, an electronic control unit (ECU) for the transmission responds by controlling solenoids, for example, utilizing a shifting logic for the selected range, and thereby executes the shift control. In such shift control, an angle of rotation of an element which rotates with movement of a shift lever is detected by a rotational position sensor, and on the basis of the output signal of the sensor, the ECU determines and confirms the selected range.
Conventional rotational position sensors include a non-contact type position sensor which detects without contact, the rotation angle of a movable-side terminal attached to a manual shaft rotated by a shift lever. The movable-side terminal is rotated together with the manual shaft, and its angle of rotation is detected and a voltage corresponding to the rotational angle is output by the non-contact sensor.
The ECU compares the output value from the non-contact type position sensor with a predetermined value (i.e. a threshold value) for each range, which predetermined value is set in advance and consists of a voltage value. Then, the ECU recognizes the pattern of the range and thus determines the selected range. Such a non-contact type rotational position sensor can generate stable output over the long term because there is little abrasion. (See, for example, U.S. Pat. No. 5,846,160.)
Non-contact type rotational position sensors are also used in other automotive applications. One example is a non-contact type throttle-opening sensor for detecting throttle opening, i.e. angle of rotation of a throttle valve in an internal combustion engine. The non-contact type throttle-opening sensor includes two Hall effect transistors as detection elements (“detectors”). These two Hall effect transistors have input-output characteristics with different absolute values for inclination of a linear output. If the relationship of the output voltages of the two Hall effect transistors is outside of a predetermined range for error in a map, it is determined that one of the Hall effect transistors has failed.
Also, if output voltage from a Hall effect transistor is outside of a predetermined tolerance range, it is determined that this detection element has failed. In the same manner, if output voltage from the other detection element is outside of a predetermined tolerance range, it is determined that this transistor has failed. Further, if a Hall effect transistor has failed, driving control of a throttle valve is performed with output voltage of the other normally operating Hall effect transistor. See, for example, Japanese laid open patent application number 2001-174212.